RRKM

The Rice–Ramsperger–Kassel–Marcus (RRKM) theory is a theory of chemical reactivity. It was developed by Rice and Ramsperger in 1927 and Kassel in 1928 (RRK theory) and generalized (into the RRKM theory) in 1952 by Marcus who took the transition state theory developed by Eyring in 1935 into account. These methods enable the computation of simple estimates of the unimolecular reaction rates from a few characteristics of the potential energy surface.

Assume that the molecule consists of harmonic oscillators, which are connected and can exchange energy with each other.

Assume that A^* is an excited molecule:

where P stands for product, and A^‡ for the critical atomic configuration with the minimum energy E₀ along the reaction coordinate.

Unimolecular rate constant ${\displaystyle k_{\mathrm {uni} }}$ is obtained as follows.

  ${\displaystyle k_{\mathrm {uni} }={\frac {1}{hQ_{r}Q_{v}}}\int \limits _{E_{0}}^{\infty }\mathrm {d} E\sum _{J=0}^{\infty }{\frac {(2J+1)G^{\ddagger }(E,J)\exp \!\left({\frac {-E}{k_{b}T}}\right)}{1+{\frac {k(E,J)}{\omega }}}}}$

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